Conventionally, a viscous heater used in a vehicular heating apparatus is disclosed in Japanese Unexamined Patent Publication (KOKAI) No.2-246,823. In regard to this viscous heater, a front housing and a rear housing are disposed so as to face each other, and fastened together by through bolts, thereby forming therein a heat-generating chamber, and a water jacket which is disposed around an outer region of the heat-generating chamber. In the water jacket, circulating water is circulated so that it is taken in through a water inlet port and that it is delivered out to an external heating circuit through a water outlet port. In the front housing, a driving shaft is held rotatably via a bearing device. On this driving shaft, a rotor is fixed so that it can rotate in the heat-generating chamber. A wall surface of the heat-generating chamber and an outer surface of the rotor constitute labyrinth grooves which approach to each other. In a space between the wall surface of the heat-generating chamber and the outer surface of the rotor, a viscous fluid, such as a silicone oil, is disposed.
In this viscous heater assembled into a vehicular heating apparatus, when the driving shaft is driven by an engine, the rotor is rotated in the heat-generating chamber. Accordingly, the viscous fluid is caused to generate heat by shearing in the space between the wall surface of the heat-generating chamber and the outer surface of the rotor. The heat thus generated is transferred to the circulating water in the water jacket, and the heated circulating water is used in the heating circuit, to heat a cabin of a vehicle or the like.
In the above conventional viscous heater, however, when a sufficient volume of viscous fluid to make a rotor completely immersed therein is contained in order to improve heat generating efficiency by using the rotor with a certain radius effectively, the viscous fluid is expanded in generating heat and tends to leak from the heat-generating chamber to the outside of the housing.
In this respect, it is conceivable to employ a construction in which the heat-generating chamber communicates with the atmosphere in order to allow expanded viscous fluid to be absorbed by the atmosphere. In this case, however, because moisture in the atmosphere tends to be supplied to the viscous fluid and degrade the viscous fluid, a decrease in heat-generating efficiency is expected. Therefore, it is not preferable to employ this type of construction.
It is an object of the present invention to provide a viscous heater which can attain an improvement in heat-generating efficiency, while preventing leakage caused by expansion of the viscous fluid.